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EBSD-Like Orientation Measurements on Selected Grains by Optical Microscopy

20 Pages Posted: 10 Jan 2020 First Look: Under Review

See all articles by Wang Xiaogang

Wang Xiaogang

Nanyang Technological University (NTU) - School of Mechanical and Aerospace Engineering

Gao Shubo

Nanyang Technological University (NTU) - School of Mechanical and Aerospace Engineering

Ekta Jain

Nanyang Technological University (NTU) - School of Mechanical and Aerospace Engineering

Matteo Seita

Nanyang Technological University (NTU) - School of Mechanical and Aerospace Engineering

Abstract

Mapping crystallographic quantities on the surface of polycrystalline metals has always been the prerogative of electron-based microscopy techniques, such as electron backscatter diffraction (EBSD). EBSD plays a central role in the study of structure-property relationships of crystalline solids, owing to its ability to correlate lattice orientation and misorientation with the geometry of the material's constituent grains at a high spatial resolution. In this work, we demonstrate the capability of performing EBSD-like orientation and misorientation measurements using an optical microscopy technique. This technique, which we call directional reflectance microscopy (DRM), allows circumventing the diffraction barrier of optical lenses by quantifying the orientation-dependent reflectance of metal surfaces. We demonstrate DRM on chemically etched polycrystalline aluminum samples. The etching process yields the formation of etch-pits comprising facets with known crystallography, which only reflect light under certain illumination angles. By analyzing the surface directional reflectance, we infer the orientation of the etch-pit facets and thus that of the underlying crystal lattice. Because of the complex reflection of light at etch-pits, DRM measurements are currently limited to a subset of grains that share the same (111) out-of-plane orientation. We compute an average difference of ~4° in the 3D crystal orientation of these grains when we measure it by EBSD and DRM. Our results set the stage for an "optical version" of EBSD, which will enable high-throughput and low-cost grain orientation mapping of polycrystalline solids.

Keywords: Optical metallography, Directional reflectance microscopy, Grain orientation measurements, intragranular misorientation distribution

Suggested Citation

Xiaogang, Wang and Shubo, Gao and Jain, Ekta and Seita, Matteo, EBSD-Like Orientation Measurements on Selected Grains by Optical Microscopy. Available at SSRN: https://ssrn.com/abstract=3513106

Wang Xiaogang (Contact Author)

Nanyang Technological University (NTU) - School of Mechanical and Aerospace Engineering

Singapore, 639798
Singapore

Gao Shubo

Nanyang Technological University (NTU) - School of Mechanical and Aerospace Engineering

Singapore, 639798
Singapore

Ekta Jain

Nanyang Technological University (NTU) - School of Mechanical and Aerospace Engineering

Singapore, 639798
Singapore

Matteo Seita

Nanyang Technological University (NTU) - School of Mechanical and Aerospace Engineering

Singapore, 639798
Singapore

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